The hydrodynamic and mass transfer parameters in water, in several types of tower-loop air-lift bioreactor were investigated. The following configurations of the apparatus were used for experiments: <internal-loop> with <central draft tube>, internal-loop with static mixers in the draft tube, <external-loop> with various circulation tube diameters (0 more thet Ad/Ar more thet 1), external-loop with perforated plates in the main zone (multistage reactor). The highest kla coefficients were-loop with perforated plates in the main zone (multistage reactor). The highest kla coefficients were obtained in external-loop multistage reactor. Ad/Ar ratio had significant influence on the main process parameters: <gas holdup>, <liquid circulation velocity>, <volumetric oxygen> transfer coefficient and mixing time.